The present invention relates to steam generators. More particularly, it relates to a steam generator which has a spirally wound flow pipe provided with a water inlet and a steam outlet and that forms an enclosure structure which bounds a hollow inner space, at least one oil or gas burner having its exhaust directed into the hollow space, an inner housing which surrounds the jacket with a bottom distance therefrom and a first annular gap therebetween so that the first gap communicates with an exhaust gas opening, and an intermediate housing which surrounds the inner housing also with a bottom distance therefrom and a second annular gap therebetween, so that the second gap communicates with a blower for supplying combustion air to the burner.
The steam generator is formed as a fully automatic device. After turning on a water pump and completely filling the flow pipe with water, as well as after attaining a predetermined water pressure, the burner is set into operation with simultaneous air supply, and steam will be generated. A pressure regulator, pressure maintaining valves, a pressure limiting member, a starting pressure valve and a temperature limiting member are used for regulating the steam generation and steam temperature, so that the regulation of the fuel supply and combustion air supply are performed automatically and constantly maintain the steam generation, the steam pressure and the temperature at adjusted values. Preheated water with temperatures of approximately between 90.degree. C. and 100.degree. C. is supplied into the flow pipe in such steam generators, especially in the region of water inlet of the pipe, to avoid that the temperature falls below the point of condensation, therefore to avoid any resulting corrosion phenomena.
In the steam generators known heretofore, the blower aspirates the combustion air from the surrounding atmosphere and guides it through the second annular gap between the inner housing and the intermediate housing upwardly to the burner. The combustion air which flows upwardly through the second annular gap is preheated through the wall of the inner housing by smoke or combustion gases which flow in the first annular gap between the inner housing and the jacket formed by the spirally wound flow pipe upwardly to the exhaust gas outlet conduit.